Black Lives Matter activists, who organized national protests surrounding killings of black Americans, including Baltimore's Freddie Grey, have challenged presidential candidates to state their position on issues surrounding race and police brutality.

Uber CEO Travis Kalanick manages a $41 billion company that has changed the transportation landscape, and shows no sign of slowing its expansion. In 2015 he introduced new services including UberPool and UberCommute.

Abu Bakr al-Baghdadi is the leader of the Islamic extremist group ISIS, which has claimed responsibility and inspired deadly terrorist attacks around the globe, including those in Paris and San Bernardino, California. The U.S. State Department in 2011 announced a reward of up to $10 million for information leading to his capture or death.

Iranian President Hassan Rouhani signed a deal with six global leaders limiting his country's nuclear program in exchange for the lifting of economic sanctions. His work to improve economic relations with the West was bolstered by a November trip to Europe.

Last year, TIME's Person of the Year were the Ebola fighters, who worked to contain the deadliest Ebola outbreak in history.

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